Context: I have a 2007 S and was having cylinder #1 misfires during idle. Compression test showed 50psi less in cylinder 1 than the other cylinders but the leakdown test yield 0% leakage in that cylinder. It was suggested that I do a valve adjustment since the valves tend to be very tight particularly on DBW models. I did the valve adjustment and all the valves were too tight. After I was done I pulled the fuse to reset the ECU multiple times and got the check engine light (same cylinder 1 misfire code) each time. Also the cabin, exhaust, and engine bay started smelling of gas fumes after I let it idle.

I bought an OBD2 code reader and reset codes that way. This time when I turned on the ignition, no engine codes/misfires at idle. I let it idle until the fans came on, no more gas smell in the cabin, or the exhaust. Light gas smell in the engine bay but that might be residual. My theory is the engine was running rich to be conservative, before it started "learning" since I reset ECU. I'm wondering if the code was actually the original misfire code and that it never got reset until I did it through the code reader. Is this possible? Or was the code actually a new code every time I reset it? I'm wondering if something changed in the DBW cars that doesn't clear the check engine light after pulling the fuse.

 

You remember the what the error numbers were?

 

Cylinder #1 Misfire P0301

 

How tight were the exhaust valves? This will tell a great deal.

 

Very tight, as low as 0.05"

 

Adjust valves to proper gap, engine stone cold. Then do a leak-down test.

 

You close to burnt valve range. Hopefully you caught it in time.

 

Thanks, I did the adjustment after leaving the car outside over night. What's the purpose of doing the leak-down test again? Why would the valve adjustment change the result?

 

If the exhaust valves are burnt --- you may have air leak to the exhaust pipe. Test with each engine cylinder at TDC. Adjustment hopefully, improves the seal enough to prevent this leak. Do the leak-down, at normal operating temp.

http://www.hotrod.com/how-to/engine/...akdown-tester/